1. Field of the Invention
The present invention relates to a sole, especially an external sole for a boot intended for sports that require a movement of the foot and/or for gliding sports. The invention is also related to a method for manufacturing soles and a boot provided with such a sole, respectively, a boot provided with a sole obtained by such a manufacturing method.
2. Description of Background and Relevant Information
As mentioned hereinabove, the present invention relates to sports requiring movement of the foot, such as hiking, skating or conventional cross country skiing, alpine skiing, telemark skiing or snowshoeing. It also applies to gliding sports, such as ice skating, roller skating with or without in-line wheels, snowboarding or skateboarding.
The aforementioned sports have common requirements with respect to the boot, and especially to the sole, which requirements are, at the outset, incompatible.
In fact, all of these sports require a shifting of the user's center of gravity from the heel zone of the user's foot to the so-called metatarsophalangeal area of natural bending of the foot, and vice versa. This shifting serves to direct and/or propel the user's body, for example, by means of edge setting or equivalent operations, such as the movement impulse performed by striding with a roller skate, or of the cross country ski, whether with the conventional technique or the skating technique. This shifting of the center of gravity is accompanied by a transmission of forces in the heel zone, on the one hand, and in some cases, by a bending in the metatarsophalangeal bending zone, on the other hand.
This generates the requirement for a good transmission of the forces, without any losses by shock-absorption and deformation in the area comprised between at least the heel and the metatarsophalangeal zone and, consequently, a requirement for rigidity of the sole in this zone, often accompanied by a requirement for as natural a movement as possible and, therefore, for flexibility associated with the sole in the metatarsophalangeal zone.
Generally, the sport boot sole is formed in one piece. The thickness of the sole is generally varied in order to vary the rigidity thereof in the longitudinal direction.
It is obvious that the integration of the two different, and even incompatible, requirements in one element, i.e., the sole, can only be performed to the detriment of one of these requirements, i.e., the transmission of the forces coming from the leg in the zone comprised between the heel and metatarsophalangeal zone and/or the flexibility in the latter zone.
The resulting problem is that this construction of the sole cannot meet all of the requirements at the same time, and it usually represents an unsatisfactory compromise between rigidity and flexibility.
Another problem concerns the manufacture of soles of the aforementioned type in one piece. These soles entail high manufacturing costs, because it is necessary to provide soles, of specific and various lengths, for all the desired sizes. This results in a necessity of manufacturing and storing a large number of different soles, or of cutting the edges of a sole to manufacture a smaller size. This latter technique, which is only used for the wear soles is a waste of material and, in reality, does not lower the production costs.
In the document No. U.S. Pat. No. 2,581,524, it is proposed to manufacture a midsale in two parts. However, this sole is adapted to a boot for spare-time activities and, therefore, the rear part remains flexible, although it has a higher rigidity with respect to the front part. The flexibility and a certain shock absorption in the rear portion are obtained by making it out of materials such as cork, sawdust or latex. The known sole of this document is therefore not capable of transmitting forces intended for edge setting, for example, and does not provide a satisfactory solution to the problems described hereinabove.